/*
Add 4 bytes to index ? 

Goal: newnews, duplicates, lookups, fast expires.
Keep '1' history index, but 'n(4)' history files.
Process the last 'm' history files each night (typically 2) to merge & clean
Sort index every night (into 300 piles, sort piles in memory, then write out)
Pre-extend history file(s) and history indexes.
Keep in memory cache of last 'nK' items for duplicate processing and dual feeds.
Hash index, 64K, 12 entries in each slot.
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  History Index format:
    int seekto; char n; char hash1; short hash2; int next;

  History Index Index: (built on startup from history index maybe?)
    hash[]  int firstentry, int nentries, int lastentry;

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newnews ... (Modify to open each file in order)
duplicates ... (10/second, 600/minute, hashed cache of last 2000 history entries) 200K 
	(check channel cache and general cache)
	Seek in history index, read 'n' items, check them, seek again if necessary.
lookups, seek thru history index

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On my ide  drive, history lookups for 100mb index, would take 5-10% of time
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100mb/12 = 10Million entries.  

